Abstract: In petrochemical production, hydrogenation unit is a high-pressure hydrogen device, which is prone to accidents of high-pressure materials backflowing to low-pressure systems. The lesson of the "3.12" high-pressure materials backflowing to low-pressure accident of the hydrogenation unit in a SINOPEC enterprise in 2018 is very profound. In order to prevent the high pressure materials from flowing back to the low pressure system, risk assessment should be carried out on the process flow, equipment and system interlock to find out the risk points of accidents and formulate safe and reliable preventive measures. Through design modification, hidden dangers can be eliminated to ensure that the device meets the intrinsic safety conditions and to nip the dangers in the bud.

Key words: hydrogenation unit, high-pressure materials backflowing to low-pressure system, risk matrix, interlocking system